In the mixing and aeration of large bodies of liquid, several different types of mixers have been used, such as floats and pumps. Generally, the floatation types have heretofore been insufficiently controllable in most directions of flow for efficient mixing. Further, most aeration apparatuses used in combination with mixers require various compressors as to applying a source of air to the mixer wherein the compressed air is injected into the liquid medium through nozzles and the like. The compressors generally expend great amounts of energy and increase the total cost of operation of the system.
In other applications, pumps and the like have been used, but these often do not provide sufficient rates of flow for the efficient mixing required in the equalization basins, as well as oxidation ditches, sludge holding tanks and other special applications. Mixers are also used in aerated lagoons in which biological solids are in equilibrium with applied waste. The basin is of sufficient depth, normally six to twelve feet and oxygen is furnished by mechanical aeration to create a turbulence level sufficient to provide adequate liquid mixing. As a result of the mixing, uniform distribution of the waste and dispersal of the oxygen is achieved to promote efficient waste biodegradation.
Aspirating mixers have heretofore been used in aerated sewage logoons, as exemplified by our previous U.S. Pat. No. 4,514,343 for an Aspirating Horizontal Mixer. This aspirator, and other aspirators, require a constriction in order to create a low pressure zone immediately downstream of the constriction, which draws air through a plenum and air intake pipe extending above the surface of the water. However, a problem is noted with such a system in that large sized foreign objects may be drawn in to the nozzle and may block or clog in the constriction, thereby shutting off the flow of water through the nozzle.
In view of the above, the present aspirating aeration and liquid mixing apparatus has been particularly directed to low cost in manufacture, efficient operation, reliability in use, and is designed for mounting upon a mast extending into the body of liquid. The present mixer is of a design permitting total oxygen dispersion throughout an entire basin at relatively low power levels generally not obtainable in the past by the use of prior art devices. Moreover, the present mixer can be used in conjunction with existing surface and subsurface aeration and mixing devices.